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miri: layout should not affect CTFE checks (outside of validation) #55142

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Oct 18, 2018
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miri: layout should not affect CTFE checks (outside of validation) #55142

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3 changes: 0 additions & 3 deletions src/librustc_mir/interpret/operand.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -688,9 +688,6 @@ impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M>
rval: OpTy<'tcx, M::PointerTag>,
) -> EvalResult<'tcx, (u128, usize)> {
trace!("read_discriminant_value {:#?}", rval.layout);
if rval.layout.abi.is_uninhabited() {
return err!(Unreachable);
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Since this is unreachable (pun intended), can you change this into an assert?

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I am not sure if it is unreachable. But I am sure that the behavior we want is to treat such enums like all the others.

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Discussed in https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/subject/unreachable-discriminant/near/135957117

gist: the code is unreachable right now, but probably not in the future. Also empty enums aren't special and we'll fail on attempting to read their discriminant, so everything is good.

}

match rval.layout.variants {
layout::Variants::Single { index } => {
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